Kenya has launched an investigation after researchers claimed HIV-positive women were being routinely sterilised without their consent in government hospitals.

A study by the African Gender and Media Initiative, based on interviews with 40 women, suggested the practice was widespread and ongoing.

Ruth Achieng, 30, was admitted to Kenyatta hospital in Nairobi in 2004 for what she thought was a routine operation after a miscarriage. She was informed afterwards that she would no longer be able to have children.

"The doctor told me that I was HIV-positive and had no reason to get more children," she said.

Another woman, 31-year-old Priscka Akuma, accused her doctor of sterilising her during a caesarean section in 2007. She said she was not told about the procedure until she complained to another member of staff about severe pain in her stomach.

"That doctor asked me if I knew that I had a tubal ligation [sterilisation]," she said. "When I found out what that meant, I asked why they did it. They said it was because I was HIV-positive and disabled and now I wouldn't bring any more problems to my community."

The report also includes examples of coercive tactics used by medical staff to obtain consent – for instance, threatening to withhold antiretroviral medication or baby milk if the woman did not agree to the procedure.

HIV-positive women are at minimal risk – less than 5% – of transmitting HIV to their child if they are given antiretroviral medication during their pregnancy and do not breastfeed, according to the World Health Organisation and UNAids.

Many of the women interviewed described the disintegration of their marriages after their operations.

Achieng and Akuma, who live in a slum outside Nairobi, said they had suffered crippling physical side effects after the surgery.

Achieng, who cleans clothes for a living, said she had not been able to climb stairs since her operation and sometimes bled constantly for a month. Akuma said she suffered from back aches and nausea, and could no longer lift heavy objects.

Most of the operations took place in government-run hospitals. But one woman claimed she was sterilised without her consent at a mobile clinic run by the family planning charity Marie Stopes.

In a statement, Marie Stopes said that informed consent was "fundamental" to its practice and that it believed the testimonials included in the report to be "a very small and … unrepresentative sample."

Carol Odada, of Women Fighting Aids in Kenya, who helped with the research, said some of the women were hoping to take legal action against the government and hospitals.

"[In the report] we used the testimonies of 40 women who were very sure that they had been forcibly sterilised," said Odada. "But there were more than 100 women in our focus group in Nairobi. Many of them don't know their rights and just believe their doctors. We have a saying here: the doctor is a second God."

Health authorities promised to investigate. "These allegations are very serious and the Kenya Medical Practitioners and Dentists Board is going to investigate them before appropriate action is taken," Shariff Shahnaz, the director of public health, told the Daily Nation newspaper.